Apparatus and Method for Determining the Thermal Stability of Fluids

ABSTRACT

A thermal oxidation tester is shown for determining thermal stability of a fluid, particularly hydrocarbons when subjected to elevated temperatures. The tendency of the heated fluid to oxidize and (1) form deposits on a surface of a heater tube and (2) form solids therein, are both measured at a given flow rate, temperature and time. The measured results are used to determine whether a fluid sample passes or fails the test. Results of measurements are recorded in a memory device on one end of the heater tube on which the deposits were made.

CROSS REFERENCE TO RELATED APPLICATIONS

None

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to methods and devices for measuring the thermalcharacteristics of fluids. Specifically, this invention relates to themethods and devices for measuring the thermal oxidation tendencies offuels used in liquid hydrocarbon-burning engines.

2. Background Art

When engines were developed for use in jet aircraft, problems began todevelop for jet fuel due to poor fuel thermal stability. At highertemperatures, the jet fuels would oxidize and form deposits that wouldclog fuel nozzles and fuel filters. These deposits would also collect inthe jet engine.

While various tests were devised and used in the 1950s and 60s to ratethe thermal oxidation characteristics of jet fuels prior to being usedin jet aircraft, Alf Hundere developed the apparatus and method whichbecame the standard in the industry. In 1970, Alf Hundere filed whatbecame U.S. Pat. No. 3,670,561, titled “Apparatus for Determining theThermal Stability of Fluids”. This patent was adopted in 1973 as ASTMD3241 Standard, entitled “Standard Test Method for Thermal OxidationStability of Aviation Turbine Fuels”, also known as the “JFTOT®Procedure”. This early Hundere patent was designed to test thedeposition characteristics of jet fuels by determining (1) deposits onthe surface of a heater tube at an elevated temperature and (2)differential pressure across a filter due to collection of particulatematter. To this day, according to ASTM D3241, the two criticalmeasurements are still (1) the deposits collected on a heater tube and(2) differential pressure across the filter due to the collection ofparticulate matter on the filter.

According to ASTM D3241, 450 mL of fuel flows across an aluminum heatertube at a specified rate, during a 2.5 hour test period at an elevatedtemperature. Currently six different models of JFTOT®¹ instruments areapproved for use in the ASTM D3241-09 Standard. The “09” refers to thecurrent revision of the ASTM D3241 Standard. 1 JFTOT is the registeredtrademark of Petroleum Analyzer Company, LP.

While over the years various improvements have been made in theapparatus to run the tests, the basic test remains the same.Improvements in the apparatus can be seen in U.S. Pat. Nos. 5,337,599and 5,101,658. The current model being sold is the JFTOT 230 Mark III,which is described in further detail in the “Jet Fuel Thermal OxidationTester—User's Manual”. The determination of the deposits that occur onthe heater tube can be made visually by comparing to known colorstandards or can be made using a “Video Tube Deposit Rater” sold underthe Alcor mark.

The determination of the amount of deposits formed on the heater tube atan elevated temperature is an important part of the test. The currentASTM D3241 test method requires a visual comparison between the heatertube deposits and known color standard. However, this involves asubjective evaluation with the human eye. To take away the subjectivityof a person, an electronic video tube deposit rater was developed.

Also, there has been considerable discussion as to the polish or finishof the heater tube. (See U.S. Pat. No. 7,093,481 and U.S. PatentApplication Publication No. US 2002/083,760.) The finish of the heatertube is very important in determining the amount of fuel deposits thatwill form thereon. Therefore, it is important that the quality of thefinish on heater tubes made today be consistent with the finish ofheater tubes made since 1973.

Once the thermal oxidation stability test has been performed on a batchof fuel, the recorded information and the heater tube are preserved toshow the batch of fuel was properly tested. The information that wasrecorded when testing a batch of fuel is maintained separately from theheater tube itself. This can cause a problem if one or the other getsmisplaced or lost. Inaccurate information and/or conclusions occur ifthe wrong set of data is associated with the wrong heater tube.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus andmethod for testing thermal oxidation stability of fluids, particularlyaviation fuels.

It is another object of the present invention to provide an apparatusand method to measure the tendency of fuels to form deposits when incontact with heated surfaces.

It is another objective of the present invention to provide an apparatusand method for testing the thermal oxidation tendency of fuels utilizinga test sample to determine if solid particles will form in the fuel atan elevated temperature and pressure.

It is another objective of the present invention to provide an apparatusand method for determining thermal oxidation stability of a batch ofaviation fuel by testing a sample at an elevated temperature andpressure to determine (1) deposits that form on a metal surface and (2)solid particles that form in the fuel.

It is another objective of the present invention to provide an apparatusand method for recording and storing the thermal oxidation tendency dataof fuels in single location.

It is yet another objective of the present invention to provide anintelligent heater tube on which a thermal oxidation stability test isperformed with deposits collecting thereon and a memory device on oneend of the intelligent heater tube to record all of the testinformation.

It is another objective of the present invention to have an intelligentheater tube with a memory device on one end thereon on which all of thetest information in association with that heater tube can be recorded.

It is another object of the present invention to provide a memory devicefor an intelligent heater tube that has a ground and data connectionwith the memory device being connected to the heater tube.

It is another object of the present invention to provide an apparatusand method for testing thermal oxidation tendencies of high performancefuels with the test results being written into a memory device on anintelligent heater tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general block diagram of a thermal oxidation stability testapparatus illustrating flow and electrical controls.

FIGS. 2 and 2A are a more detailed block diagram showing a thermaloxidation test apparatus used to perform ASTM D3241 Standard.

FIG. 3 is a pictorial diagram of the coolant flow for FIGS. 2 and 2A.

FIG. 4 is a pictorial diagram of the airflow in FIGS. 2 and 2A

FIG. 5 is a pictorial diagram showing flow of the test sample in FIGS. 2and 2A.

FIG. 6 is a lengthwise view of an intelligent heater tube.

FIG. 7 is an exploded perspective end view of the intelligent heatertube of FIG. 6, showing the EEPROM in broken lines inside of a memorydevice on the intelligent heater tube.

FIG. 8 is an elevated view of the 1-Wire EEPROM used in the memorydevice of FIG. 7.

FIG. 9 is a pictorial illustration of how to record data on the memorydevice of an intelligent heater tube.

FIG. 10 is a schematic diagram of the writer module used to write on a1-Wire EEPROM.

FIG. 11 is a schematic diagram of a built-in Video Tube Deposit Raterfor use with an intelligent heater tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic block diagram of a thermal oxidation stabilitytester referred to generally by the reference numeral 20. The thermaloxidation stability tester 20 has an embedded computer 21 with a touchscreen 23 for user interface. While many different types of programscould be run, in the preferred embodiment, Applicant is running C++ inthe embedded computer 21. The touch screen 23 displays all of theinformation from the thermal oxidation stability tester 20 that needs tobe conveyed to the user. The user communicates back and forth with theembedded computer 21 through the touch screen 23. If a batch of fuel isto be tested, a test sample is put in the sample delivery system 25.

It is important to the test to make sure the test sample is oxygensaturated through aeration. Therefore, the embedded computer 21 operatesa sample aeration control 31 for a period of time to make sure thesample is fully aerated. The aeration of the sample takes place at thebeginning of the test.

The embedded computer 21 turns on a sample flow control 27, which is apump used to deliver the sample throughout the thermal oxidationstability tester 20. Simultaneous with the sample flow control 27pumping the test sample throughout the system, sample pressure control29 maintains a fixed pressure throughout the system. It is important tomaintain pressure in the system to prevent boiling of the test samplewhen at elevated temperatures. In the present thermal oxidationstability tester 20, the sample is maintained at approximately 500 psiwhen undergoing the thermal oxidation stability test.

Also, the embedded computer 21 controls parameters affecting theintelligent heater tube 33. The test data is recorded to the intelligentheater tube 33 via intelligent heater tube writer 35 from the embeddedcomputer 21. Critical test parameters are recorded on a memory device(as described subsequently) on an end of the intelligent heater tube 33via the intelligent heater tube writer 35. The rating of the depositformed on the intelligent heater tube 33 will be recorded on the memorydevice at a later time.

In performing the thermal oxidation stability test on a test sample, theintelligent heater tube 33 is heated by tube heater control 37. The tubeheater control 37 causes current to flow through the intelligent heatertube 33, which causes it to heat up to the temperature setpoint.

To prevent the hot intelligent heater tube 33 from heating other partsof the thermal oxidation stability tester 20, bus-bar coolant control 39provides coolant upper and lower bus-bars holding each end of theintelligent heater tube 33. This results in the center section of theintelligent heater tube 33 reaching the prescribed temperature while theends of the intelligent heater tube 33 are maintained at a lowertemperature. This is accomplished by flowing coolant via the bus-barcoolant control 39 across the ends of the intelligent heater tube 33.

The test parameters, such as the dimension of the heater tube, pressureof the test sample or flow rate are fixed by ASTM D3241. However, thecontrol of the equipment meeting these parameters are the focus of thisinvention.

Referring now to FIGS. 2 and 2A in combination, a schematic flow diagramis shown connecting the mechanical and electrical functions. Theembedded computer 21 and the touch screen 23 provide electrical signalsas indicated by the arrows. A test sample is contained in the samplecontainer 41. To make sure the sample in the sample container 41 isfully aerated, an aeration pump 43 is turned ON. The aeration pump 43pumps air through a dryer 45 where the air is dehumidified to removemoisture. From the dryer 45, a percent relative humidify sensor 47determines the humidity level of the pumped air and provides thatinformation to the embedded computer 21. Assuming the percent humidityof the pumped air is sufficiently low, the test procedure will continuepumping air through the flow meter 49 and aeration check valve 50 intothe sample container 41. During aeration, flow meter 49 should recordapproximately 1.5 liters of air per minute. Since the flow meter 49 runsfor approximately six minutes, the aeration pump 43 will spargeapproximately nine liters of air into the test sample. This issufficient time to saturate the test sample with dry air.

Within the sample container 41, a sample temperature measurement 51 istaken and provided to the embedded computer 21. The sample temperaturemeasurement 51 is to ensure that the test sample is between 15°-32° C.If the test sample is outside of this temperature range, results can beimpacted. Therefore, if the test sample is outside this temperaturerange, the embedded computer 21 would not let the test start.

Once the test sample has been aerated and if all the other parametersare within tolerance, then the sample drive pump 53 will turn ON. Thesample drive pump 53 is a single piston HPLC pump, also known as ametering pump. With every stroke of the piston, a fixed volume of thesample is delivered. The speed of the sample drive pump 53 is controlledso that it pumps 3 mL/min of the test sample. The sample drive pump 53is configured for fast refill which minimizes the need for manual pumppriming. Pulsations, associated with pumps of this design are minimizedwith the use of a pulse dampener and a coil tubing on the outlet side aswill be subsequently described.

To get air out of the tubing between the sample container 41 and thesample drive pump 53 at the start of the test, an auto pump primingvalve 55 is opened, a sample vent valve 54 is closed and the aerationpump 43 is turned ON by the embedded computer 21. The auto pump primingvalve 55 opens and remains open while a combination of sample and air isdischarged into waste container 57. At the same time the aeration pump43 provides positive pressure in the sample container 41 to force testsample from the sample container 41 to the sample drive pump 53. Thesample vent valve 54 closes to prevent venting of the air pressure toatmosphere to maintain a pressure of 2 to 3 psi. A sample vent checkvalve 56 across the sample vent valve 54 opens at 5 psi to prevent thepressure in the sample container 41 from exceeding 5 psi. Once thesample drive pump 53 starts pumping the test sample, auto pump primingvalve 55 will close and the sample vent valve 54 will open. Thereafter,the sample drive pump 53 will pump the test sample through check valve59 to the prefilter 61. The check valve 59 prevents fluid from flowingbackwards through the sample drive pump 53. The check valve 59 operatesat a pressure of approximately 5 psi. The check valve 59 preventssiphoning when the sample drive pump 53 is not pumping. Also, checkvalve 59 prevents fluid from being pushed backwards into the sampledrive pump 53.

The prefilter 61 removes solid particles in the test sample that couldaffect the test. The prefilter 61 is a very fine filter, normally in theorder of 0.45 micron in size. The purpose of the prefilter 61 is to makesure particles do not get into the test filter as will be described. Theprefilter 61 is replaced before every test.

From the prefilter 61, the test sample flows through an inlet 63 intothe cylindrical heater tube test section 65. Outlet 67, whileillustrated as two separate outlets, is actually a single outlet at theupper end of the cylindrical heater tube test section 65. Extendingthrough the cylindrical heater tube test section 65 is the intelligentheater tube 69, sealed at each end with ceramic bushings and an o-ring(not shown). While the test sample flows through the cylindrical heatertube test section 65 via inlet 63 and outlet 67 and around theintelligent heater tube 69, the housing of the cylindrical heater tubetest section 65 is electrically isolated from the intelligent heatertube 69. Only the test sample comes in contact with the center sectionof the intelligent heater tuber 69. Inside of the intelligent heatertube 69 is a thermocouple 71 that sends a signal back to the embeddedcomputer 21 as to the temperature of the center section of theintelligent heater tube 69.

Test sample flowing from the cylindrical heater tube test section 65flows through a differential pressure filter 73, commonly called the“test filter”. In a manner as will be explained in more detail, theintelligent heater tube 69 heats up the test sample inside of thecylindrical heater tube test section 65 to the test parameter set point.Heating of the test sample may result in degradation of the test sample,or cause solid particles to form. The solid particles may deposit on thecenter section of the intelligent heater tube 69, and/or may collect onthe differential pressure filter 73. The pressure drop across thedifferential pressure filter 73 is measured by differential pressuresensor 75. Pressure across the differential pressure filter 73 iscontinuously monitored by the embedded computer 21 through thedifferential pressure sensor 75. When the pressure across thedifferential pressure filter 73 exceeds a predefined differential ofapproximately 250 mm to 280 mm of mercury, the differential pressurebypass valve 77 opens to relieve the pressure. By test definition,exceeding a differential pressure of 25 mm Hg results in failure of thetest.

For this test to be performed, the test sample must remain as a liquid.At typical testing temperatures of 250° C. to 350° C., many hydrocarbonfuels will transition to the vapor phase at ambient pressures. To keepthe test sample in the liquid phase, the back pressure regulator 79maintains approximately 500 psi pressure in the system. This systempressure is monitored by the system pressure sensor 81, which reportsinformation to the embedded computer 21. During a test, normal flow of atest sample is through differential pressure filter 73 and through theback pressure regulator 79. From the back pressure regulator 79, thetest sample flows through sample flow meter 83 to waste container 57.The sample flow meter 83 accurately measures the flow rate of the testsample during the test. The sample flow meter 83 provides sample flowrate information to the embedded computer 21.

A system/safety vent valve 85 is connected into the system andcontrolled via the embedded computer 21. The system/safety vent valve 85acts to relieve excess system pressure in the case of power loss,improperly functioning system components or other system failures. Inthe event of this occurrence, the system pressure sensor 81 sends asignal to the embedded computer 21, triggering the system/safety ventvalve 85 to open and relieve excess pressure. Also, at the completion ofa test, the system/safety vent valve 85 opens to vent pressure from thesystem. The system/safety vent valve 85 is normally set to the openposition requiring a program command from the embedded computer 21 toclose the system/safety vent valve 85. Therefore, if power is lost, thesystem/safety vent valve 85 automatically opens.

At the end of the test, after the system/safety vent valve 85 is openedand system pressure is relieved, the flush air pump 87 turns ON andflushes air through flush check valve 89 to remove the test sample fromthe system. The flush air pump 87 pushes most of the test sample out ofthe system via the system/safety vent valve 85 into the waste container57.

The system may not operate properly if there are air pockets or airbubbles in the system. During a test, it is important to maintain anair-free system. Therefore, at the beginning of each test, the solenoidoperated differential pressure plus vent valve 91 and the differentialpressure minus vent valve 93 are opened, flushed with test sample, andvented to remove any air pockets that may be present. During thebeginning of each test, the position of the differential pressure ventvalves 91 and 93 ensure there is no air in the differential pressurelines.

If the waste container 57 is properly installed in position, a signalwill be fed back to the embedded computer 21 indicating the wastecontainer 57 is correctly connected. This also applies for the samplecontainer 41 which sends a signal to the embedded computer 21 when it isproperly connected. The system will not operate unless both the wastecontainer 57 and the sample container 41 are properly positioned.

The center portion of the intelligent heater tube 69 is heated to thetest parameter set point by flowing current through the intelligentheater tube 69. Instrument power supplied for current generation and allother instrument controls is provided through local available power 95.Depending on local power availability, local available power 95 may varydrastically. In some areas it is 50 cycles/sec. and in other areas it is60 cycles/sec. The voltage range may vary from a high of 240 Volts downto 80 Volts or less. A universal AC/DC converter 97 takes the localavailable power 95 and converts it to 48 Volts DC. With the universalAC/DC converter 97, a good, reliable, constant 48 Volts DC is generated.The 48 Volts DC from the universal AC/DC converter 97 is distributedthroughout the system to components that need power through the DC powerdistribution 99. If some of the components need a voltage level otherthan 48 Volts DC, the DC power distribution 99 will change the 48 VoltsDC to the required voltage level.

To heat the intelligent heater tube 69, the 48 Volts from the universalAC/DC converter 97 is converted to 115 Volts AC through 48 Volt DC/115Volts AC inverter 101. While taking any local available power 95,running it through a universal AC/DC converter 97 and then changing thepower back to 115 Volts AC through a 48 Volts DC/115 Volts AC inverter101, a stable power supply is created. From the 48 Volts DC/115 Volts ACinverter 101, power is supplied to the heater tube module 103. Theheater tube module 103 then supplies current that flows through theintelligent heater tube 69 via upper clamp 105 and lower clamp 107. Theheater tube module 103 is controlled by the embedded computer 21 so thatduring a normal test, the thermocouple 71 inside of the intelligentheater tube 69 will indicate when the intelligent heater tube 69 hasreached the desired temperature.

While the center section of the intelligent heater tube 69 heats todesired test set point, the ends of the intelligent heater tube 69should be maintained near room temperature. To maintain the ends of theintelligent heater tube 69 near room temperature, a coolant flowsthrough an upper bus-bar 109 and lower bus-bar 111. The coolant insidethe upper bus-bar 109 and lower bus-bar 111 cools the upper clamp 105and lower clamp 107 which are attached to the ends of the intelligentheater tube 69. The preferred cooling solution is a mixture ofapproximately 50% water and 50% antifreeze (ethylene glycol). As thecoolant flows to the coolant container 115, the flow is measured by flowmeter 113. To circulate the coolant, a cooling pump 117 pumps thecoolant solution into a radiator assembly 119. Inside of the radiatorassembly 119, the coolant is maintained at room temperature. Theradiator fan 121 helps remove heat from the coolant by drawing airthrough the radiator assembly 119. From the radiator assembly 119, thecoolant flows into the lower bus-bar 111 then through upper bus-bar 109prior to returning via the flow meter 113.

The flow meter 113 is adjustable so that it can ensure a flow ofapproximately 10 gal./hr. The check valve 123 helps ensure the coolingsystem will not be over pressurized. Check valve 123 will open at around7 psi, but normally 3-4 psi will be developed when running the coolantthrough the entire system.

To determine if the intelligent heater tube 69 is shorted out to thehousing (not shown in FIGS. 2 and 2A), a heater tube short detector 110monitors a short condition. If a short is detected, the embeddedcomputer 21 is notified and the test is stopped.

On one end of the intelligent heater tube 69 there is a memory device125 to which information concerning the test can be recorded by IHTwriter 127 as will be discussed in more detail. While a test is beingrun on a test sample, the IHT writer 127 will record information intothe memory device 125. At the end of the test, all electronicinformation will be recorded onto the memory device 125 of theintelligent heater tube 69, except for the manual tube deposit rating.To record this information, the intelligent heater tube 69 will have tobe moved to another location to record the deposit rating either (a)visually or (b) through a Video Tube Deposit Rater. At that time, asecond IHT writer will write onto the memory device 125. The Video TubeDeposit Rater may be built into the system or may be a standalone unit.

The intelligent heater tube 69 is approximately 6¾″ long. The ends areapproximately 3/16″ in diameter, but the center portion that is heatedis approximately ⅛″ in diameter. Due to very low electrical resistanceof aluminum, approximately 200 to 250 amps of current flows through theintelligent heater tube 69. Both the voltage and the current through theintelligent heater tube 69 is monitored by the embedded computer 21, butalso the temperature of the center section of the intelligent heatertube 69 is monitored by the thermocouple 71 which is also connected tothe embedded computer 21. The objective is to have the center section ofthe intelligent heater tube 69 at the required temperature. To generatethat type of stable temperature, a stable source of power is providedthrough the universal AC/DC converter 97 and then the 48 VDC/115 VACinverter 101. By using such a stable source of power, the temperature onthe center section of the heater tube 69 can be controlled within acouple of degrees of the required temperature.

Referring now to FIG. 3 of the drawings, a pictorial representation ofthe coolant flow during a test is illustrated. Like numbers will be usedto designate similar components as previously described. A pictorialillustration of the heater tube test section 129 is illustrated on thelower left portion of FIG. 3. Coolant from the radiator assembly 119 isprovided to the lower bus-bar 111 and upper bus-bar 109 via conduit 131.From the upper bus-bar 109, the coolant flows via conduit 133 to flowmeter 113. From flow meter 113, the coolant flows through conduit 135 tothe coolant container 115. The cooling pump 117 receives the coolantthrough conduit 137 from the coolant container 115 and pumps the coolantinto radiator assembly 119. If the pressure from the cooling pump 117 istoo high, check valve 123 will allow some of the coolant to recirculatearound the cooling pump 117. FIG. 3 is intended to be a pictorialrepresentation illustrating how the coolant flows during a test.

Likewise, FIG. 4 is a pictorial representation of the aeration systemfor the test sample. Similar numbers will be used to designate likecomponents as previously described. An aeration pump 43 pumps airthrough conduit 139 to a dryer 45. The dryer 45 removes moisture fromthe air to prevent the moisture from contaminating the test sampleduring aeration. From the dryer 45, the dried air will flow throughconduit 141 to humidity sensor 47. If the percent relative humidity ofthe dried air blowing through conduit 141 exceeds a predetermined amountof 20% relative humidity, the system will shut down. While differenttypes of dryers 45 can be used, it was found that Dry-Rite silica geldesiccant is an effective material for producing the desired relativehumidity.

From the percent humidity sensor 47, the dried air flows through conduit143 to flow meter 49, which measures the air flow through conduit 143and air supply conduit 145. From air supply conduit 145, the dried airflows through aeration check valve 50 and conduit 146 sample containerarm mounting clamp 147 and sample container arm 149 to aeration conduit151 located inside of sample container 41. In the bottom of samplecontainer 141, a glass frit 153 connects to aeration conduit 151 tocause the dried air to sparge through the test sample in samplecontainer 41. When the sample container 41 is in place and the samplecontainer arm 149 is connected to the sample container arm mounted clamp47, contact 155 sends a signal to the embedded computer 21 (see FIG. 2)indicating the sample container 41 is properly installed.

Referring now to FIG. 5, a pictorial illustration of the flow of thetest sample in connection with FIGS. 2 and 2A is shown in a schematicflow diagram. The test sample is contained in sample container 41, whichis connected via sample container arm 149 to the sample container armmounting clamp 147. Vapors given off by the test sample are dischargedthrough a vent 157, normally through a vent hood to atmosphere.Simultaneously, the sample drive pump 53 draws some of the test sampleout of the sample container 41. The sample drive pump 53 is a singlestroke HPLC pump connected to a pulse dampener 159. While the pulsedampener 159 may be configured a number of ways, the pulse dampener 159in the preferred configuration has a diaphragm with a semi-compressiblefluid on one side of the diaphragm. This fluid is more compressible thanthe test sample thereby reducing pressure changes on the test sampleflow discharged from the sample drive pump 53. The sample drive pump 53is connected to auto pump priming valve 55. During start-up, the closedauto pump priming valve 55 opens until all of the air contained in thepump and the lines are discharged into the waste container 57. In caseit is needed, a manual priming valve 161 is also provided. Additionally,the aeration pump 43 (see FIG. 2) is turned ON to provide a slightpressure in the sample container 41 of about 2 to 3 psi. The sample ventvalve 54 closes to prevent this pressure from escaping to atmosphere.This pressure will help push the fluid sample from the sample container41 to the inlet of the sample drive pump 53. The 5 psi check valve 56prevents the pressure in the sample container exceeding 5 psi. Duringthe test, coil 163 also provides further dampening in addition to thepulse dampener 159. Check valve 59 ensures there is no back flow of thesample fuel to the sample drive pump 53. However, at the end of a test,flush check valve 89 receives air from flush air pump 87 to flush thetest sample out of the system.

During normal operation of a test, the sample fuel will flow throughcheck valve 59 and through a prefilter 61 removing most solid particles.Following the prefilter 61, the test sample flows into the heater tubetest section 129 and then through the differential pressure filter 73.Each side of the differential pressure filter 73 connects to thedifferential pressure sensor 75. Also connected to the differentialpressure filter 73 is the back pressure regulator 79. The pressure onthe system is continuously monitored through the system pressuretransducer 81. If for any reason pressure on the system needs to bereleased, system/safety vent valve 85 is energized and the pressurizedtest sample is vented through the four-way cross connection 165 to thewaste container 57.

At the beginning of the test, to ensure there is no air contained in thesystem, the differential pressure plus vent valve 91 and thedifferential pressure minus vent valve 93 are opened to vent anypressurized fluid through the four-way cross connection 165 to the wastecontainer 57.

In case the differential pressure filter 73 clogs so that thedifferential pressure exceeds a predetermined value, differentialpressure bypass valve 77 will open to relieve the pressure.

To determine the exact flow rate of the test sample through the system,the sample flow meter 83 measures the flow rate of test sample from theback pressure regulator 79 before being discharged through the wastecontainer arm 167 and the waste container clamp 169 into the wastecontainer 57. The waste container 57 is vented all the time through vent171.

Intelligent Heater Tube (IHT)

The intelligent heater tube (IHT) 69 is shown in FIG. 6. The intelligentheater tube 69 is cylindrical in shape as described previously. The top173 and bottom 175 are 3/16″ in diameter. The test section 177 is ⅛″ indiameter. Extending longitudinally along the center axis of theintelligent heater tube 69 is a center bore 179. The thermocouple 71(previously described in conjunction with FIG. 2A) is located inside thecenter bore 179. At the end of the enlarged bottom 175 is a memorydevice 125. The memory device 125 is slightly smaller in diameter thanthe heater tube bottom 175.

As shown in FIGS. 7 and 8 in combination with FIG. 6, an EEPROM 181 islocated inside of the memory device 125. The EEPROM 181 only has a datasignal and a ground signal. The ground signal connects to ground stick183 and the data signal connects to data plate 185. The ground stick 183fits inside of the center bore 179 of the intelligent heater tube 69.The EEPROM 181 is contained inside of insulated housing 187 of thememory device 125. The data plate 185 is on the end of the insulatedhousing 187 and is slightly smaller in diameter than the insulatedhousing 187. The only two connections to the memory device 125 arethrough the ground stick 183 and the data plate 185.

While the EEPROM 181 has a total of six solder connections 189, only twoof them are connected to either the ground stick 183 or data plate 185.The data plate 185 is made from a material that will not tarnish easilysuch as phosphorous bronze or beryllium copper. The entire memory device125 is resistant to degradation from jet fuel or related materials. Toensure there is no accidental electrical connection, the data plate 185is slightly smaller in diameter than the insulated housing 187 of memorydevice 125, which in turn is slightly smaller in diameter than theenlarged bottom 175 of the intelligent heater tube 69.

Referring to FIG. 9, a pictorial example of how to connect to the memorydevice 125 of the intelligent heater tube 69 when running a test of asample fuel is shown. The intelligent heater tube 69 is held in positionby lower clamp 107. The ground stick 183 of the EEPROM 181 is containedinside of center bore 179 of the enlarged bottom 175.

To write to and from the EEPROM 181, an IHT writer 127 as shown inconnection with FIG. 2A is used. The IHT writer 127 has a data line thatconnects to a spring-loaded contact 191 that pushes against, and makeselectrical contact with, the data plate 185. The other side of the IHTwriter 127 connects to ground via lower clamp 107, intelligent heatertube 69 and ground stick 183. The output from the IHT writer 127 caneither go directly to the JFTOT, to a video tube deposit rater, or to apersonal computer. Normally, there will be two IHT writers 127. One IHTwriter 127 will be located inside of a jet fuel thermal oxidationstability tester (JFTOT®). Another IHT writer 127 will be used to recordthe deposit information as collected on the test section 177 of theintelligent heater tube 69 as is recorded either (a) manually from avisual inspection or (b) with the Video Tube Deposit Rater. The IHTwriter 127 when installed on the test apparatus only communicates withthe embedded computer 21 shown in FIG. 2. After the test has been run,the only information lacking on the memory device 125 is recording theheater tube deposit rating. This will be recorded either from a manualinspection of the intelligent heater tube 69 or from a video tubedeposit rater, either of which will require a separate IHT writer module127.

Referring now to FIG. 10, the IHT writer module 127 is shown in moredetail. The IHT writer module 127 uses 5 Volts DC as its normal power. AUSB port 193 is used to connect the IHT writer 127. USB port 193 hasfour wires for a positive supply voltage VCC, a negative voltage D−, apositive voltage D+ and a ground GND. Also, the IHT writer 127 has a RS232 port 195 with four wires being used to transmit data TXD, receiveddata RXD, ground GND, and positive supply voltage VCC. From the IHTwriter 127, one wire is for data and one wire is for ground which areused when connecting to the memory device 125 containing the EEPROM 181.The USB port 193 and the RS 232 port 195 supplies data through the IHTwriter 127 to the memory device 125. Inside of the IHT writer 127 is aUART TTL level 197 that converts the data to the appropriate form tocommunicate to EEPROM 181. The abbreviation UART stands for “UniversalAcrosynchrinous Receiver/Transmitter”. TTL is an abbreviation for“Transistor-Transistor Logic”.

The JFTOT 230 Mark III can be configured with or without a Video TubeDeposit Rater, to work with the intelligent heater tube 69 having thememory device 125 as shown in the combination of FIGS. 10 and 11. Theembedded computer 21 connects through RS 232 port 195 to the secondintelligent heater tube writer 201, which is similar to IHT writer 127.If the test system does not have a video tube deposit rater module, thenIHT writer 203 may be used to write to the memory device 125 of theintelligent heater tube 69. In this manner, the IHT writer 203 can beused to manually input the data into the memory device 125.

On the other hand, if the testing apparatus does have a Video TubeDeposit Rater, RS 232 port 196 connects the embedded computer 21 to theVideo Tube Deposit Rater (VTDR) module 205. By pressing the eject/closedevice 207, the door of the VTDR module 205 will open and theintelligent heater tube 69 may be inserted. By pushing the start button209, deposits collected on the intelligent heater tube 69 during thetest are rated. The rating is automatically recorded onto the EEPROMchip 181 (not shown in FIG. 11) contained in the memory device 125.

Also, the image data from the VTDR module 205 may be retrieved by VTDRLAN connection 211.

It is important to remember that two different IHT writer modules areused in the full system. One writer module is used while the heater tubeis in the run position. The other writer module is used when the depositrating is being recorded.

After the information has been recorded on the memory device 125,eject/close device 207 is pressed to open the door to allow removal ofthe intelligent heater tube 69. Now, all of the information recordedfrom that test is contained with the intelligent heater tube 69. Sincemost users keep the recorded data and the heater tube, this allows bothto be archived together

1. An apparatus for testing thermal oxidation stability of a test samplesuch as a hydrocarbon fuel comprising: a source of electric power; anintelligent heater tube connected to said source of electric power forflowing current to heat a center section of said intelligent heater tubeto a predetermined temperature; a coolant flow circuit supplying coolantto each end of said intelligent heater tube to keep each end thereofnear room temperature; an aeration circuit with an aeration pump forpumping air to aerate said test simple in a sample container; a testsample flow circuit for flowing said test sample around said centersection to heat said test sample to said predetermined temperature, saidtest sample flow circuit including: sample drive pump pumping said testsample from said sample container around said center section of saidintelligent heater tube; a differential pressure filter in said testsample flow circuit after said intelligent heater tube to filter out anysolids that may have formed in said test sample when heated to saidpredetermined temperature due to oxidation of said test sample; adifferential pressure sensor for measuring differential pressure acrosssaid differential pressure filter; a back pressure regulator formaintaining said test sample being pumped by said sample drive pump at atest pressure high enough to keep said test sample in a liquid phasewhen heated to said predetermined temperature; waste container forcollecting such hydrocarbon fuel after said test; a memory device onsaid intelligent heater tube for first recording of said differentialpressure therein.
 2. The apparatus for testing thermal oxidationstability of said test sample as recited in claim 1 further comprising afirst writer for receiving and writing into said memory device saiddifferential pressure.
 3. The apparatus for testing thermal oxidationstability of said test sample as recited in claim 2 further comprising arater for comparing (a) deposits on said center section of saidintelligent heater tube occurring during said heating of said testsample to said predetermined temperature against (b) known standards and(c) second recording of said comparison in said memory device via asecond writer.
 4. The apparatus for testing thermal oxidation stabilityof said test sample as recited in claim 3 wherein said memory deviceincludes an EEPROM with a ground and data connection for said first andsecond recording therein.
 5. The apparatus for testing thermal oxidationstability of said test sample as recited in claim 4 wherein said memorydevice is connected to an end of said intelligent heater tube by saidground connection, a data connection being on an opposite end of saidmemory device from said ground connection.
 6. The apparatus for testingthermal oxidation stability of said test sample as recited in claim 5wherein the diameter of said memory device is slightly less than thediameter of said intelligent heater tube to form a shoulder therebetween.
 7. The apparatus for testing thermal oxidation stability ofsaid test sample as recited in claim 3 wherein said rater is a videotube deposit rater, after running the test said intelligent heater tubebeing moved to said video tube deposit rater with said second writertherein for said comparison and said second recording therein.
 8. Theapparatus for testing thermal oxidation stability of said test sample asrecited in claim 5 further including a spring loaded contact for makingelectrical connection with said data connection during said firstrecording and said second recording to allow recording there through. 9.A method of testing a test sample in liquid form for thermal oxidationstability comprising the following steps: aerating said test sample in asample container with dry air to saturate said test sample with oxygen;heating a center section of an intelligent heater tube to apredetermined temperature by flowing current there through; cooling eachend of said intelligent heater tube by flowing coolant from a coolantflow circuit to said each end; pumping said test sample at a low flowrate around said center section of said intelligent heater tube so thattemperature of said test sample is raised to approximately saidpredetermined temperature; test filtering with a differential pressurefilter said test sample to collect solids formed in said test samplewhen heated to said predetermined temperature; maintaining an elevatedpressure on said test sample during said pumping step sufficient to keepsaid test sample from evaporating; discharging said test sample to awaste container; and first recording results from the preceding steps ina memory device attached to said intelligent heater tube.
 10. The methodof testing the test sample in liquid form for thermal oxidationstability as recited in claim 9 wherein said first recording occursduring said preceding step and thereafter a second recording occurs whencomparing deposits on said center section of said intelligent heatertube to known standards.
 11. The method of testing the test sample inliquid form for thermal oxidation stability as recited in claim 10,wherein said first recording and said second recording occurs atdifferent times and locations.
 12. The method of testing the test samplein liquid form for thermal oxidation stability as recited in claim 9includes an initial step of automatic pump priming to eliminate airpockets or bubbles in said test sample prior to said pumping step,wherein manual pump priming is not required.
 13. The method of testingthe test sample in liquid form for thermal oxidation stability asrecited in claim 9 includes after said discharging step venting toremove said elevated pressure from said test sample.
 14. The method oftesting the test sample in liquid form for thermal oxidation stabilityas recited in claim 9 wherein said aerating step includes a drying stepto remove moisture from air to get said dry air.
 15. The method oftesting the test sample in liquid form for thermal oxidation stabilityas recited in claim 9 includes a further step of prefiltering solids outof said test sample before said pumping around said center section ofsaid intelligent heater tube and said heating to said predeterminedtemperature.
 16. The method of testing the test sample in liquid formfor thermal oxidation stability as recited in claim 9 includes anadditional step of measuring flow rate of said test sample before saiddischarging step.
 17. The method of testing the test sample in liquidform for thermal oxidation stability as recited in claim 13 includesafter said venting step a step of flushing said test sample.
 18. Themethod of testing the test sample in liquid form for thermal oxidationstability as recited in claim 9 wherein said coolant flow circuitincludes a coolant pump for circulating said coolant and a radiator forremoving heat from said coolant.
 19. The method of testing the testsample in liquid form for thermal oxidation stability as recited inclaim 9 wherein said heating step includes creating a stable source ofpower for said current.
 20. The method of testing the test sample inliquid form for thermal oxidation stability as recited in claim 10wherein said first and second recording in said memory device is on anEEPROM therein with a ground and data connection.
 21. The method oftesting the test sample in liquid form for thermal oxidation stabilityas recited in claim 20 wherein said memory device is attached by saidground to one end of said intelligent heater tube, an opposite side ofsaid memory device having a data plate for said data connection.
 22. Themethod of testing the test sample in liquid form for thermal oxidationstability as recited in claim 21 wherein said memory device is smallerin diameter than said intelligent heater tube.
 23. An intelligent heatertube for testing thermal oxidation stability of a test sample whenheated to a predetermined temperature by a source of current flowingthere through, results from a test being in electronic form, saidintelligent heater tube comprising: an elongated cylindrical body havinga narrow center section and enlarged cylindrical portions on both ends,said enlarged cylindrical portions for clamping to said source ofcurrent, said center section being polished and receiving deposits fromsaid test sample when said test sample is elevated to said predeterminedtemperature by said current flowing through said center section and saidtest sample is flowing there around; a memory device attached to one endof said intelligent heater tube for receiving said results of said testin said electronic form.
 24. The intelligent heater tube for testingthermal oxidation stability of test samples as recited in claim 23wherein said memory device has a ground stick and a data plate onopposite ends thereof, said ground stick being electronically connectedto said intelligent heater tube.
 25. The intelligent heater tube fortesting thermal oxidation stability of test samples as recited in claim24 wherein said ground stick inserts into a center opening in saidelongated cylindrical body.
 26. The intelligent heater tube for testingthermal oxidation stability of test samples as recited in claim 25wherein cross sectional diameter of said memory device is less than saidenlarged cylindrical portions.
 27. The intelligent heater tube fortesting thermal oxidation stability of test samples as recited in claim23 wherein said memory device includes an EEPROM chip contained within acylindrical housing.
 28. The intelligent heater tube for testing thermaloxidation stability of test samples as recited in claim 27 furtherincludes a ground stick extruding from said EEPROM and said cylindricalhousing, said ground stick being in electrical contact with saidintelligent heater tube, a data plate on an opposite end of saidcylindrical housing from said ground stick for said receiving of saidresults of said test.